An emulsified composition may contain both an oily component and an aqueous component, and hence being excellent as a skin external preparation. In general, an emulsion is prepared using a surfactant, but some of surfactants with low molecular weights may irritate the skin or may be partially decomposed to generate substances that irritate the skin (Patent Document 1). Therefore, there has been developed a technology for using a polymer compound having an emulsifying effect, such as an alkyl acrylate/methacrylate copolymer instead of the surfactant with a low molecular weight (Patent Documents 2 and 3). However, in the emulsifying technology using an alkyl acrylate/methacrylate copolymer, an emulsified composition is stabilized by ion repulsion of a carboxyl group, and hence, there may be a case where the pH varies with time during storage, and stability of the preparation deteriorates.
In view of such circumstances, an emulsified composition having both of safety and stability has been studied. For example, there has been developed an emulsified composition containing an alginic acid polyol ester, sodium alginate, and calcium chloride (Patent Document 4). The emulsified compositions are constantly stable under a certain temperature condition (40° C., about two weeks) to be employed in a general storage stability test for a cosmetic or the like.
However, in the case of the skin external preparation such as a cosmetic, the form of the preparation may change in some cases by long-term exposure to an unexpected severe high-temperature condition or the like during storage in distribution stage and at home, and the stability of the preparation is not enough yet.
Meanwhile, a 4-alkylresorcinol such as 4-n-butylresorcinol is known to have an effect of suppressing melanin production, and there is also known a technology for blending the substance in a skin external preparation to provide a skin-whitening effect (Patent Document 5, Non-Patent Document 1, etc.). In addition, there is known the fact that addition of a 4-alkylresorcinol and an unsaturated higher alcohol ether compound of a polyol can produce a stable emulsified composition (Patent Document 6) and a technology for obtaining an emulsified composition that is stable and has low viscosity by using an alkyl acrylate/methacrylate copolymer as an emulsifier (Patent Document 7).
On the other hand, it is not known that in an emulsified composition, which contains an alginic acid polyol ester such as alginic acid propylene glycol, a 4-alkylresorcinol can prevent a decrease in the viscosity of the composition, and a prescription using the compounds in combination has not been studied.    Patent Document 1: JP 07-149621 A    Patent Document 2: JP 10-265332 A    Patent Document 3: JP 2003-073281 A    Patent Document 4: JP 2004-196728 A    Patent Document 5: JP 02-49715 A    Patent Document 6: JP 2000-327557 A    Patent Document 7: JP 2001-10925 A    Non-Patent Document 1: Under the editorship of Takeda et al., “Usability of cosmetics, progress, and future prospect of evaluation technology”, YAKUJI NIPPO LIMITED, published on Mar. 31, 2001